# How is Work and Power Related? Chapter 5 Work and Power - PowerPoint PPT Presentation

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## How is Work and Power Related? Chapter 5 Work and Power

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### How is Work and Power Related? Chapter 5 Work and Power Goals: define and calculate work, energy, kinetic energy, potential energy, power and use the concept of ... – PowerPoint PPT presentation

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Title: How is Work and Power Related? Chapter 5 Work and Power

1
How is Work and Power Related? Chapter 5 Work and
Power
• Goals define and calculate work, energy, kinetic
energy, potential energy, power and use the
concept of conservation of energy

2
What is Work? Section 5.1
• Work is a transfer or conversion of energy
• transfer occurs when a force is applied in the
direction of the force force
mass x acceleration (g)
• conversion occurs from one form of energy to
another
• mechanical, thermal, electrical, radiant,
nuclear and chemical
• W F x d W F x d cos ?

3
Simple Machines demonstrate the concept and
calculations of Work
• Simple Machine- device that makes work easier
• multiply force OR distance
• Increasing force or distance are at the expense
of the other variable
• Energy is conserved in an ideal situation
no friction
• Work in would equal Work out in another words F
x d (in) F x d (out)
• Work in is done on the machine and Work out is
done by the machine

4
• R ---2m-----f--------4m------- E
• MA 2
• R 40N---------f------------------- E 20N
• MA 2
• MA Fr / Fe or
• MA Xe / Xr
• Levers include 1st, 2nd, 3rd, classes, wheels and
axels and pulleys
• Pulley- grooved wheel and a rope MA the number
of strands supporting resistance

5
• Inclined Planes include ramps, wedges and screws
• Gears- toothed wheels MA ratio of teeth of each
gear increase force or speed of rotation
• Efficiency- ratio of work out to work in
• eff W out / W in

6
What is Energy? 5.2
• Energy ability to cause a change
• to do work work transfer of energy
• 6 forms of energy and two states of energy
• Kinetic motion
• W F x d
• m x a x ?X a ?X vf² - vi² / 2
• m x vf² - vi² / 2
• ½ m v²
• increase mass vs increase velocity v²

7
• Work Energy Theorem
• transfer of energy by a force through a distance
• transfers Kinetic Energy
• Work ?KE
• KE f KE i
• Units KE ½ mv²
• kg m²/s²
• N m
• J

8
What is Potential Energy?
• Potential Energy state of energy where a change
is stored
• position relative to a measured height
• gravitational potential energy
• PE m g h weight m g
• kg m/s² m N
• N m
• J

9
• Elastic potential energy energy stored in an
object stretched or compressed
• Spring ex. spring scale
• PE elastic ½ k x²
• k spring constant
• x distance stretched

10
How is Energy Conserved ?
• Conserved energy is not gained or lost within a
system
• only converted or transferred
• Mechanical Energy is the sum of the KE and the PE
in a system
• the exception is friction that converts some ME
into heat that is nonmechanical
• ME i ME f KE PE KEtotal
• ½ mv² mgh ½ mv² mgh
• ex. Falling rock PE to PEKE to KE

11
What is the Rate at which work is done?
• Power the rate at which work is done or energy
converted or transferred
• P ?W / t
• F x d / t
• F x v
• mgh / t or ½ mv² / t
• units P W / t
• J / s
• watts 1000 w
kw
• 1 hp 746 w

12
• YOU have the POWER
• To get the WORK done
• And
• Accelerate on this next Exam